Method for processing a substrate comprising a silicon nitride layer

Abstract

A substrate processing method according to the present application is a substrate processing method for selectively etching a silicon nitride layer in a substrate in which a silicon oxide layer and a silicon nitride layer are alternately stacked, including a step of plasma-izing a plurality of gases and plasma-etching the silicon nitride layer, the plurality of gases including a first gas containing fluorine other than nitrogen trifluoride and a second gas containing hydrogen, and an atomic ratio of fluorine to hydrogen included in the plurality of gases is adjusted to control an etching profile in a thickness direction of the silicon nitride layer. According to the substrate processing method according to the present application, the etching profile of the silicon nitride layer can be adjusted, the plasma-ization efficiency of the etching gas is increased, and radicals can sufficiently reach a lowermost nitride layer.

Description

TECHNICAL FIELD

[0001] The present application relates to a substrate processing method. More specifically, the present application relates to a substrate processing method capable of adjusting the etching profile of a silicon nitride layer formed on a substrate. BACKGROUND

[0002] Recently, with the miniaturization of semiconductor elements, semiconductor elements have become increasingly highly integrated. Since a silicon nitride film is used as a dielectric film or an insulating film having stable chemical properties, it is widely used in not only a basic element separation process of a memory element but also a contact process or a capping process for a dynamic random access memory (DRAM) and a FLASH Memory manufacturing process for use as a sidewall raw material or the like.

[0003] On the other hand, in manufacturing semiconductor elements, there are cases where a multilayered silicon oxide film and a silicon nitride film are formed on a substrate. In this case, in order to selectively etch the silicon nitride film, an etchant having a high etching selectivity compared to the silicon oxide film should be applied.

[0004] Conventionally, a phosphoric acid-based etchant is known as an etchant having a high etching selectivity compared to the silicon oxide film. Etching of the silicon nitride film using the phosphoric acid-based etchant belongs to wet etching. However, wet etching has a problem that the etchant penetrates into an element pattern due to surface tension and etching cannot be smoothly performed to the lowermost nitride film. This problem further becomes serious as the number of layers of semiconductor elements becomes larger and the pattern becomes finer.

[0005] As an alternative to such wet etching, dry etching is proposed. Dry etching is a method of plasma-izing an etching gas and etching a silicon nitride film using etching radicals generated thereby. As an etching gas for performing etching of a silicon nitride film, carbon tetrafluoride (CF4), nitrogen trifluoride (NF3), or the like is proposed.

[0006] On the other hand, a hydrogen-containing etching gas such as monofluoromethane (CH3F) or difluoromethane (CH2F2) is not much used in performing dry etching of a silicon nitride film, because a thick polymer film formed of hydrogen radicals is generated when the etching gas is plasma-ized. Such a thick polymer film lowers the etching rate of the silicon nitride film.

[0007] However, in the case where the formation of a polymer film is to be suppressed and only a hydrogen-free etching gas is used, the etching selectivity of the silicon nitride film with respect to the silicon oxide film is not high, and thus there is a problem that the silicon oxide film is also etched to some extent.

[0008] [Patent Document]

[0009] [Patent Literature]

[0010] [Patent Literature 1] Korean Patent Laid-Open Publication No. 10-2013-0056039 (Published on May 29, 2013) SUMMARY

[0011] [Problems to be Solved by the Invention]

[0012] An object of the present application is to provide a substrate processing method which can perform selective etching of a silicon nitride layer with respect to a silicon oxide layer, and which can adjust the etching profile in the thickness direction of the silicon nitride layer by controlling the atomic ratio of fluorine to hydrogen included in an etching gas, the radio frequency (RF) frequency, and the like.

[0013] [Technical Means for Solving the Problems]

[0014] A substrate processing method according to an embodiment of the present application for solving the above problem is a substrate processing method which selectively etches a silicon nitride layer in a substrate in which a silicon oxide layer and a silicon nitride layer are alternately stacked, characterized by comprising a step of plasma-etching the silicon nitride layer using a plurality of gases, the plurality of gases including a first gas containing fluorine other than nitrogen trifluoride (NF3) and a second gas containing hydrogen, and adjusting the atomic ratio of fluorine to hydrogen included in the plurality of gases to control the etching profile in the thickness direction of the silicon nitride layer.

[0015] The atomic ratio of the fluorine to the hydrogen (F:H) can be 15:1 to 35:1.

[0016] The first gas is carbon tetrafluoride (CF4), and the second gas can be one or more selected from the group consisting of difluoromethane (CH2F2), monofluoromethane (CH3F), methane (CH4), hydrogen (H2), ammonia (NH3), and trifluoromethane (CHF3).

[0017] The plurality of gases can additionally include nitrogen and oxygen.

[0018] The plasma etching can be performed under a radio frequency frequency of 15 MHz or more and less than 60 MHz.

[0019] The plasma etching can be performed in a Capacitively Coupled Plasma (CCP) mode.

[0020] A substrate processing method according to another embodiment of the present application for solving the above-described problem is a substrate processing method of selectively etching a silicon nitride layer in a substrate in which silicon oxide layers and silicon nitride layers are alternately stacked, characterized by comprising the step of: plasma-etching the silicon nitride layers in a manner such that the etching rate of the uppermost silicon nitride layer is the same as the etching rate of the lowermost silicon nitride layer or the etching rate gradually increases from the uppermost silicon nitride layer to the lowermost silicon nitride layer, using a plurality of gases containing a first gas containing fluorine other than nitrogen trifluoride and a second gas containing hydrogen, and the atomic ratio (F:H) of fluorine to hydrogen contained in the plurality of gases is 22.5:1 or more and 35:1 or less.

[0021] A substrate processing method according to still another embodiment of the present application for solving the above-described problem is a substrate processing method of selectively etching a silicon nitride layer in a substrate in which silicon oxide layers and silicon nitride layers are alternately stacked, characterized by comprising the step of: plasma-etching the silicon nitride layers in a manner such that the etching rate gradually decreases from the uppermost silicon nitride layer to the lowermost silicon nitride layer, using a plurality of gases containing a first gas containing fluorine other than nitrogen trifluoride and a second gas containing hydrogen, and the atomic ratio (F:H) of fluorine to hydrogen contained in the plurality of gases is 15:1 or more and less than 22.5:1.

[0022] [Effects of the Invention]

[0023] The substrate processing method according to the present application can perform selective etching of the silicon nitride layer with respect to the silicon oxide layer by not containing nitrogen trifluoride (NF3) in the etching gas and containing a fluorine-containing gas such as carbon tetrafluoride (CF4) and a hydrogen-containing gas such as difluoromethane (CH2F2).

[0024] In particular, the substrate processing method according to the present application can adjust the etching profile of the silicon nitride layer by controlling the atomic ratio of fluorine to hydrogen contained in the etching gas to be 15:1 to 35:1.

[0025] Further, the substrate processing method according to the present application can increase the plasma efficiency of the etching gas and radicals can sufficiently reach the lowermost nitride layer by controlling the RF frequency for plasma etching to be in the range of 15 MHz or more and less than 60 MHz.

[0026] The effects of the present application are not limited to the above-mentioned effects, and another effect not mentioned can be clearly understood by those skilled in the art through the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic view illustrating an example of an etching apparatus that can be used in the present application.

[0028] Figure 2a An example of a substrate that becomes an etching target of the present application is shown.

[0029] Figure 2b An example of etching at the same etching rate from the lowermost silicon nitride layer to the uppermost silicon nitride layer is shown.

[0030] Figure 2c An example of etching at an etching rate that gradually increases from the uppermost silicon nitride layer to the lowermost silicon nitride layer is shown.

[0031] Figure 2d An example of etching at an etching rate that gradually decreases from the uppermost silicon nitride layer to the lowermost silicon nitride layer is shown.

[0032] Figure 3 The relative etching rates of the uppermost silicon nitride layer and the lowermost silicon nitride layer according to the atomic ratio of fluorine to hydrogen contained in the etching gas are shown. DETAILED DESCRIPTION

[0033] Advantages and features of the present application and methods of accomplishing the same will become apparent from the embodiments described below with reference to the accompanying drawings. However, the present application is not limited to the embodiments disclosed below, but can be implemented in various forms. The present embodiments are provided merely to complete the disclosure of the present application and to completely convey the scope of the present application to those skilled in the art, and the present application is defined only by the scope of the claims. Throughout the specification, like reference numerals in the drawings refer to the same constituent element. For the sake of clarity of explanation, the size and relative size of layers and regions in the drawings can be exaggerated.

[0034] The case where an element or layer is said to be "on" or "above" another element or layer includes not only the case where it is directly on or above the other element or layer, but also the case where it is on or above the other element or layer with other layers or elements interposed therebetween. In contrast, the case where an element is said to be "directly on" or "directly above" another element or layer means that no other element or layer is interposed therebetween. In addition, it should be understood that, in the case where a certain constituent element is said to be "connected", "joined", or "linked" to another constituent element, the constituent elements can be directly connected or linked to each other, or other constituent elements can be "interposed" between the constituent elements, or the constituent elements can be "connected", "joined", or "linked" by other constituent elements.

[0035] "Lower," "bottom," "upper," "top," and the like are used as spatial relative terms to easily describe the relationship of one element or constituent to another element or constituent as shown in the drawings. The spatial relative terms are to be understood to include terms that are not only the directions shown in the drawings but also terms that are different from each other in the directions of the elements when used or operated. For example, in the case of turning over the elements shown in the drawings, the element described as "below" another element can be placed "above" the other element. Therefore, "below" as an illustrative term can include both the lower and upper directions.

[0036] The terms used in the present specification are used to describe the embodiments, and thus are not intended to limit the present application. In the present specification, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "include" and / or "comprises" used in the specification, which describe the constituents, steps, actions and / or elements, do not exclude the presence or addition of one or more other constituents, steps, actions and / or elements.

[0037] Hereinafter, a substrate processing method according to a preferred embodiment of the present application will be described in detail with reference to the accompanying drawings as follows.

[0038] Figure 1 is a schematic view illustrating an example of an etching apparatus that can be used in the substrate processing method according to the present application.

[0039] Referring to Figure 1 , the illustrated etching apparatus includes a chamber 10, a susceptor 20, a showerhead 30, a plurality of gas supply sources 40, and an RF power source 50.

[0040] The susceptor 20 is disposed at the lower side inside the chamber 10, and the showerhead 30 is disposed at the upper side inside the chamber 10.

[0041] A substrate S as a processing target is disposed at the upper portion of the susceptor 20. The susceptor 20 can have a temperature adjusting member such as a heating wire or a cooling liquid line. In addition, the susceptor 20 can be connected to the ground.

[0042] The showerhead 30 is disposed at the upper side inside the chamber 10. The showerhead 30 functions to distribute and supply a reaction gas to the inside of the chamber 10. In addition, the showerhead 30 can function as an RF electrode so that a plasma is formed inside the showerhead or in the space between the showerhead and the susceptor. For example, in the case where a plasma is formed inside the showerhead 30, the upper portion 31 of the showerhead 30 is connected to the RF power source 50 to function as an RF electrode, and the lower portion 32 of the showerhead is connected to the ground to function as a ground electrode.

[0043] A plurality of gas supply sources 40 are arranged outside the chamber 10, and supply a plurality of gases including a fluorine-containing gas to the inside of the chamber 10. In order to perform substrate processing, a plurality of gases including a fluorine-containing gas are supplied from the plurality of gas supply sources 40 to the inside of the chamber 10 through the showerhead 30. A flow rate adjustment meter for adjusting the flow rate of each gas can be arranged between the plurality of gas supply sources 40 and the chamber 10. The plurality of gases can be mixed in advance outside the chamber and supplied to the showerhead 30, or mixed inside the showerhead 30.

[0044] The RF power source 50 can apply power having a predetermined RF frequency (e.g., 27.12 MHz, 50 MHz, etc.). After supplying a plasma ignition gas or a plurality of gases to the inside of the chamber 10 (e.g., inside the showerhead), RF power (e.g., high-frequency power) having a predetermined RF frequency in the RF power source 50 is applied to the upper portion 31 of the showerhead functioning as an electrode, thereby forming a plasma inside the showerhead 30. The case of forming a plasma can also be referred to as plasma-izing the gases supplied to the inside of the chamber.

[0045] The substrate processing method according to an embodiment of the present application includes a substrate arranging step and a silicon nitride layer etching step.

[0046] In the substrate arranging step, a substrate in which one or more silicon oxide layers and two or more silicon nitride layers are formed is arranged on a susceptor in a chamber.

[0047] Figure 2a An example of a substrate that can be used as an etching target according to the present application is shown.

[0048] Reference Figure 2a The substrate can have silicon oxide layers 210 and silicon nitride layers 220 alternately stacked on a silicon wafer 201. The silicon oxide layers 210 and the silicon nitride layers 220 can be formed, for example, as nine layers and eight layers, respectively, as shown in Figure 2a not limited thereto.

[0049] In the silicon nitride layer etching step, a plurality of gases are supplied to the inside of the chamber and two or more silicon nitride layers are selectively etched.

[0050] Figure 2b An example in which the silicon nitride layers are etched at the same etching rate from the lowermost silicon nitride layer to the uppermost silicon nitride layer is shown. Figure 2c An example in which the silicon nitride layers are etched at an etching rate that gradually increases from the uppermost silicon nitride layer to the lowermost silicon nitride layer is shown. Figure 2d An example in which the silicon nitride layers are etched at an etching rate that gradually decreases from the uppermost silicon nitride layer to the lowermost silicon nitride layer is shown.

[0051] The etching profile of the silicon nitride layers is shown in Figures 2b to 2dThe examples shown can be various. In particular, it can be necessary to etch at the same etching rate from the uppermost silicon nitride layer to the lowermost silicon nitride layer, or to gradually increase the etching rate toward the lowermost silicon nitride layer, as shown in the examples. Figure 2b Figure 2c

[0052] In the present application, as shown below, a gas containing hydrogen and a gas containing fluorine are contained in the etching gas, and the etching profile is adjusted by adjusting the atomic ratio of fluorine to hydrogen.

[0053] First, in order to perform selective etching of the silicon nitride layer, in the present application, a plurality of gases are supplied into the chamber. The plurality of gases include a first gas containing fluorine (F) and a second gas containing hydrogen (H).

[0054] On the other hand, in the present application, it is preferable to exclude nitrogen trifluoride (NF3) from the first gas. Nitrogen trifluoride (NF3) not only etches the silicon nitride layer, but also etches the silicon oxide layer to some extent, and thus it is preferable to exclude it as much as possible from the plurality of gases used for selective etching of the silicon nitride layer.

[0055] In the present application, the first gas and the second gas are plasma-ized inside the chamber, for example, inside the showerhead.

[0056] As the process conditions for performing plasma etching, it is preferable to apply high-frequency power having an RF frequency of 15 MHz or more and less than 60 MHz to the showerhead using the RF power source of the etching device, and more preferably an RF frequency of 15 MHz to 50 MHz. In the case where the RF frequency is less than 15 MHz, such as 13.56 MHz, the plasma-ization, decomposition efficiency of the plurality of gases is low, and thus most of the etching radicals are consumed in the upper side silicon nitride layer. Therefore, in the case where the RF frequency is less than 15 MHz, the etching of the lower side silicon nitride layer is difficult to proceed smoothly, and damage such as pattern collapse can occur due to over-etching of the upper side silicon nitride layer, and thus it is preferable that the RF frequency be 15 MHz or more. On the other hand, in the case where the RF frequency is 60 MHz or more, such as 60 MHz, 67.8 MHz, it can be difficult to obtain the desired etching profile due to excessive ionization, decomposition efficiency even by adjusting other process conditions.

[0057] ​​In addition, the plasma mode used in the present application is more preferably a CCP mode in an ICP mode or a CCP mode. This is because in the case of the CCP mode, uniformity is excellent compared to the ICP mode, and thus more uniform process results of the device can be obtained in large capacity substrate processing.

[0058] In addition to this, as the process conditions for performing plasma etching, an RF power of 700 W to 2500 W, a process pressure of 0.3 Torr to 10 Torr, a susceptor surface temperature of 0°C to 50°C, and the like can be proposed, but are not limited thereto, and various known process conditions can be applied.

[0059] The atomic ratio of fluorine to hydrogen (F:H) included in the plurality of gases is preferably 15:1 to 35:1. The atomic ratio of fluorine to hydrogen (F:H) can be achieved by controlling the flow rates of the fluorine-containing gas and the hydrogen-containing gas.

[0060] In the case where the atomic ratio of fluorine to hydrogen (F:H) is less than 15:1, there is too much hydrogen, and a polymer film generated by the plasma is formed thick on the surface of the silicon oxide layer and the silicon nitride layer, and thus the etching rate of the silicon nitride layer can greatly decrease. In contrast, in the case where the atomic ratio of fluorine to hydrogen (F:H) exceeds 35:1, the polymer film is formed too thin due to a lack of hydrogen, and thus the etching rate of the silicon oxide film also becomes high, and thus damage to the pattern can occur.

[0061] The first gas can be carbon tetrafluoride (CF4). The second gas can be one or more selected from the group consisting of difluoromethane (CH2F2), monofluoromethane (CH3F), methane (CH4), hydrogen (H2), ammonia (NH3), and trifluoromethane (CHF3). It is more preferable that the first gas is carbon tetrafluoride (CF4) and the second gas is difluoromethane (CH2F2). The flow rate of the first gas can be determined to be about 800 seem or less, and the flow rate of the second gas can be determined to be 200 seem or less, but is not limited thereto.

[0062] On the other hand, the plurality of gases can additionally include nitrogen and oxygen. Nitrogen is combined into NO and contributes to etching of the silicon nitride layer. In addition, oxygen contributes to removal of process byproducts. Nitrogen can be supplied into the chamber at a flow rate of, for example, 2000 seem or less, and oxygen can be supplied into the chamber at a flow rate of, for example, 3000 seem or less.

[0063] After the selective etching of the silicon nitride layer, a heat treatment for removing a condensed film formed on the surface of the silicon nitride layer can be performed during the etching. The heat treatment can be performed at a temperature in the range of 80°C to 300°C.

[0064] Embodiment

[0065] Hereinafter, the configuration and the operation of the present application will be described in more detail by preferred embodiments of the present application. However, this case is presented as a preferred example of the present application and cannot be interpreted as limiting the present application in any sense. Since what is not described herein can be technically sufficiently inferred by those skilled in the art, the description thereof will be omitted.

[0066] A substrate as shown in the example was prepared. Silicon nitride layers 220 (N) and silicon oxide layers 210 (O) were alternately stacked on a silicon wafer 201. The silicon nitride layers 220 (N) were formed in total of eight layers. The silicon oxide layers 210 (O) were formed by thermal oxidation. Figure 2a

[0067] Carbon tetrafluoride (CF4) and difluoromethane (CH2F2) were used as etching gases, and the flow rates were controlled in terms of the atomic ratio of fluorine to hydrogen (F:H) shown in Table 1. In addition thereto, the following process conditions were applied.

[0068] RF frequency of the RF power source: 27.12 MHz

[0069] RF power of the RF power source: 1000 W

[0070] Plasma mode: CCP mode

[0071] Pressure inside the chamber: 1 Torr

[0072] Temperature of the surface of the susceptor: room temperature

[0073] Table 1 shows the SiN etching rate, the SiN selectivity, and the T / B ratio of the etching rate of the uppermost silicon nitride layer to the lowermost silicon nitride layer in terms of the atomic ratio of fluorine to hydrogen (F:H).

[0074] In Table 1, the SiN etching rate and the SiO2 etching rate are values obtained by a non-pattern wafer process result.

[0075] Further, the T / B ratio indicates the etching rate of the uppermost silicon nitride layer to the lowermost silicon nitride layer. In the case where the T / B ratio is 1, the etching rates of the lowermost silicon nitride layer and the uppermost silicon nitride layer are the same. In the case where the T / B ratio is greater than 1, the uppermost silicon nitride layer is etched more than the lowermost silicon nitride layer. On the contrary, in the case where the T / B ratio is less than 1, the lowermost silicon nitride layer is etched more than the uppermost silicon nitride layer.

[0076] [Table 1]

[0077] ​

[0078] As can be seen from Table 1, in the case where the atomic ratio of fluorine to hydrogen (F:H) is less than 15:1, the etching of the lowermost silicon nitride layer is hardly performed. The case where the atomic ratio of fluorine to hydrogen (F:H) is less than 15:1 means that the hydrogen ratio is relatively high compared with other examples. Since the hydrogen ratio is very high, a polymer film derived from plasma is formed too thick on the surface of the silicon oxide layer and the silicon nitride layer when plasma etching is performed, and thus the silicon nitride layer appears to be hardly etched. Therefore, the atomic ratio of fluorine to hydrogen (F:H) is preferably 15:1 or more.

[0079] In addition, as can be seen from Table 1, in the case where the atomic ratio of fluorine to hydrogen (F:H) is more than 35:1, pattern collapse occurs. It is observed that since the hydrogen ratio is very low, a polymer film is formed thin on the surface of the silicon oxide layer and the silicon nitride layer, and thus the etching amount of the silicon oxide layer is also greatly increased, resulting in pattern collapse. Therefore, the atomic ratio of fluorine to hydrogen (F:H) is preferably 35:1 or less.

[0080] Figure 3 The relative etching rates of the uppermost silicon nitride layer and the lowermost silicon nitride layer according to the atomic ratio of fluorine to hydrogen contained in the etching gas are shown.

[0081] As can be seen from Table 1 and Figure 3 In the case where the atomic ratio of fluorine to hydrogen (F:H) is 15:1, the T / B ratio showing the etching rate of the uppermost silicon nitride layer to the lowermost silicon nitride layer is shown to be about 2.6, and in the case where the atomic ratio of fluorine to hydrogen (F:H) is 18:1, the T / B ratio is shown to be about 2.3. This case is useful as shown in Figure 2d when the etching rate of the lowermost silicon nitride layer is desired to be relatively gradually decreased toward the lowermost.

[0082] In addition, in the case where the atomic ratio of fluorine to hydrogen (F:H) is 22.5:1, the T / B ratio is shown to be about 1.0, and this case is useful as shown in Figure 2b when it is desired to make the etching rate of the uppermost silicon nitride layer and the lowermost silicon nitride layer uniform.

[0083] In addition, in the case where the atomic ratio of fluorine to hydrogen (F:H) is 25:1, 30:1, 35:1, the T / B ratio is shown to be less than 1.0, and this case is useful as shown in Figure 2c when the etching rate of the lowermost silicon nitride layer is desired to be gradually increased toward the lowermost.

[0084] In addition, it can be seen that the T / B ratio is decreased when the atomic ratio of fluorine to hydrogen (F:H) is increased from 22.5:1 to 30:1, but the T / B ratio is rather increased when the atomic ratio of fluorine to hydrogen (F:H) is increased from 30:1 to 35:1.

[0085] As described above, with the substrate processing method according to the present application, the following effects can be obtained: selective etching of a silicon nitride layer with respect to a silicon oxide layer can be performed, and by controlling the atomic ratio of fluorine to hydrogen included in the etching gas, the etching profile of the silicon nitride layer formed on the substrate can also be adjusted.

[0086] In particular, by controlling the atomic ratio of fluorine to hydrogen (F:H) to be 22.5: 1 or more and 35: 1 or less, etching can be performed uniformly from the uppermost silicon nitride layer to the lowermost silicon nitride layer in the multilayered silicon nitride layer, or etching can be performed more gradually from the uppermost silicon nitride layer toward the lowermost silicon nitride layer, and thus an etching profile as shown in Figure 2b or Figure 2c can be obtained.

[0087] On the other hand, by controlling the atomic ratio of fluorine to hydrogen (F:H) to be 15: 1 or more and less than 22.5: 1, the amount of etching gradually decreases from the uppermost silicon nitride layer toward the lowermost silicon nitride layer, and thus an etching profile as shown in Figure 2d can be obtained.

[0088] On the other hand, even when the RF frequency is fixed to 50 MHz, by adjusting the atomic ratio of fluorine to hydrogen (F:H) to be 15: 1 to 35: 1, similar T / B ratio results to those in Table 1 can be obtained.

[0089] In contrast, when the RF frequency is fixed to 60 MHz, even when the process recipe is changed with various RF powers and pressures, the thickness direction profile of the silicon nitride layer cannot be adjusted. This is due to excessive ionization and decomposition efficiency when plasma etching is performed. Therefore, from this result, it can be seen that the RF frequency suitable for the substrate processing method according to the present application is more preferably less than 60 MHz.

[0090] Although the embodiments of the present application have been described above, various changes or modifications can be made by those skilled in the art within the scope of the present application. Such changes and modifications can also belong to the present application without departing from the scope of the present application. Therefore, the scope of the present application should be judged based on the claims recited above.

Claims

1. A substrate processing method of selectively etching a silicon nitride layer in a substrate in which a silicon oxide layer and a silicon nitride layer are alternately stacked, characterized by comprising a step of plasma-etching the silicon nitride layer by plasma- izing a plurality of gases, the plurality of gases contain a first gas containing fluorine other than nitrogen trifluoride and a second gas containing hydrogen, and an atomic ratio of fluorine to hydrogen contained in the plurality of gases is adjusted to control an etching profile in a thickness direction of the silicon nitride layer.

2. The substrate processing method according to claim 1, characterized in that the atomic ratio of fluorine to hydrogen is 15: 1 to 35:

1.

3. The substrate processing method according to claim 1, characterized in that the first gas is carbon tetrafluoride, the second gas is one or more selected from the group consisting of difluoromethane, monofluoromethane, methane, hydrogen, ammonia, and trifluoromethane.

4. The substrate processing method according to claim 1 or 3, characterized in that the plurality of gases additionally contain nitrogen and oxygen.

5. The substrate processing method according to claim 1, characterized in that the plasma etching is performed at a radio frequency of 15 MHz or more and less than 60 MHz.

6. The substrate processing method according to claim 1, characterized in that the plasma etching is performed in a capacitive coupling plasma mode.

7. A substrate processing method of selectively etching a silicon nitride layer in a substrate in which a silicon oxide layer and a silicon nitride layer are alternately stacked, characterized by plasma- izing a plurality of gases, and plasma-etching the silicon nitride layer in such a manner that an etching rate of an uppermost silicon nitride layer is the same as that of a lowermost silicon nitride layer or the etching rate gradually increases from the uppermost silicon nitride layer to the lowermost silicon nitride layer, comprising the steps of: the plurality of gases contain a first gas containing fluorine other than nitrogen trifluoride and a second gas containing hydrogen, and an atomic ratio of fluorine to hydrogen contained in the plurality of gases is 22.5: 1 or more and 35: 1 or less.

8. A substrate processing method of selectively etching a silicon nitride layer in a substrate in which a silicon oxide layer and a silicon nitride layer are alternately stacked, characterized by plasma- izing a plurality of gases, and plasma-etching the silicon nitride layer in such a manner that the etching rate gradually decreases from an uppermost silicon nitride layer to a lowermost silicon nitride layer, comprising the steps of: the plurality of gases contain a first gas containing fluorine other than nitrogen trifluoride and a second gas containing hydrogen, and an atomic ratio of fluorine to hydrogen contained in the plurality of gases is 15: 1 or more and less than 22.5:

1.

9. The substrate processing method according to claim 7 or 8, characterized in that the first gas is carbon tetrafluoride, the second gas is one or more selected from the group consisting of difluoromethane, monofluoromethane, methane, hydrogen, ammonia, and trifluoromethane.

10. The substrate processing method according to claim 7 or 8, characterized in that the plasma etching is performed at a radio frequency of 15 MHz or more and less than 60 MHz. ​

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